I. The churches of Rome and Alexandria should be at one in everything.
How much of the divine love we feel for you, beloved, you will be able to estimate from this, that we are anxious to establish your beginnings on a surer basis, lest anything should seem lacking to the perfection of your love, since your meritorious acts of spiritual grace, as we have proved, are already in your favour. Fatherly and brotherly conference, therefore, ought to be most grateful to you, holy brother, and received by you in the same spirit as you know it is offered by us.
For you and we ought to be at one in thought and act, so that as we read, in us also there may be proved to be one heart and one mind. For since the most blessed Peter received the headship of the Apostles from the Lord, and the church of Rome still abides by His institutions, it is wicked to believe that His holy disciple Mark, who was the first to govern the church of Alexandria, formed his decrees on a different line of tradition: seeing that without doubt both disciple and master drew but one Spirit from the same fount of grace, and the ordained could not hand on anything else than what he had received from his ordainer.
We do not therefore allow it that we should differ in anything, since we confess ourselves to be of one body and faith, nor that the institutions of the teacher should seem different to those of the taught.
Source: Letters (New Advent)